Thanks M.B. Doc. I just had the dealer check the over-voltage relay and the coils. They could not find anything wrong here either. I am going to leave this problem for the time being. Maybe it was the coolant temp sensor that was replaced. It is just frustrating that this problem cannot be identified before so that I can aviod the risk of possibly being stranded. The next time I bring my car in for service, I will have them look at the speed sensor also if there is such a device in my car.
P.S. The hose connector on my rad already blew. I had it replaced a year ago.
Thanks everyone for your suggestions.